DPDT footswitch popping problem

[simpleobserver]

Hey guys.  I've got a Belton reverb pedal i built from their schem that I added another reverb pot to switch between, but I get that popping noise when i do.  I think there's a cap to ground thing you can do to get rid of the popping, but i don't quite understand how it works and what exactly to do.  Can someone explain it to me or give me another suggestion?  Thanks fellas.

[induction]

Please post your schematic.

[simpleobserver]

This is basically it. The two switches are really just one DPDT footswitch.  What do ya think?

[simpleobserver]

ok, i'm seeing that this layout is not very helpful at this size, let me see if i can make it bigger.   

[simpleobserver]

[bluebunny]

Looking at the path to your image, it looks like you're trying to post a picture from a Gmail account or similar?  I can't see anything.  Can anyone else?  You may need to put it somewhere else (e.g. dropbox).

[induction]

I can't see it.

[simpleobserver]

Sorry about that.  Try this.

https://www.dropbox.com/s/7idmn9l814hb3e6/Reverb%20board%20Layout%20%28TL074%29.gif

[bluebunny]

That's better!   

[simpleobserver]

It didn't pop at first, and I've switched out the switch before and it temporarily fixed the problem, so it might be as simple as i need to put a better switch in.  Plus, I've got a dual looper i built that has that same basic switching circuit that doesn't pop.  There's a cap to ground, or something, trick i've heard of, though.  I just don't quite know what it is and i wanted to try and see if that was the answer.

[induction]

I can't follow your layout.  Can you post the full schematic?  (Not just the app note, which is incomplete.)

Also, is your 78L05 output tied to ground?

[MrStab]

1M resistor between where one/both of the pots connect to the switch and ground? probably a cliché answer, but why not! lol

[simpleobserver]

This is the schem i used.  It only shows the half of the switch that switches the pot, the other half of the switch just goes from the 9v to the ground of the TL074.

https://www.dropbox.com/s/d1s3ms2kc0jgevh/reverb%20schematic%20with%20two%20switchable%20pots.jpg

[simpleobserver]

the 78L05 output is goes in to one of the lugs of the Belton unit.  It looks weird on the layout, but the 3 and 4 hole jumpers on the bottom are really the lugs of the reverb unit.

[giappui]

The switch can pop for mechanical problem or cause there's some voltage inside that

Are younsure there are no bridge? Could you try with some pull-down resistor

[simpleobserver]

The pull down resister is the 1M to ground between the switch and the pot, right?  I'll totally give that a try.

[armdnrdy]

Try adding a 1M-2.2M pulldown resistor to ground on the common lug (center lug) of the switch.

[Mike Burgundy]

This is a virtual-ground circuit, it's running on a single supply, convincing the opamps that 1/2 that supply (Vref) is "ground". Probably better to hook the 1M to Vref, that's where that bit of circuitry is DC biased. Grounding the 1M won't slam it all the way from 4.5V to ground (since the next opamp is forcing it to Vref via the 10k feedback resistor and the 39k next to it, while the split second the switch is open the large 1M  is attempting to pull to ground) but it won't help. A small difference in voltage during the switching cycle WILL result in a pop. A voltage divider of 1M and 49k (10k+39k) makes the switch lug sit at 4.3V. If you have one of the two pots at max, it will force that point to 4.5V. Difference 0.2V, big pop.

[duck_arse]

if the cmos inverter is doing nothing but powering the led, I'd ditch it, and use a proper millenium bypass setup (or a 3pdt footswitch, if you lean that way), and run that from the 9V with a series resistor and supply bypass cap.

both the 100nF at the input (1M) and the 10uF at the output (100k) already have pulldown resistors. I don't think there is many maore places within this circuit that needs pull-downing.

[armdnrdy]

both the 100nF at the input (1M) and the 10uF at the output (100k) already have pulldown resistors. I don't think there is many maore places within this circuit that needs pull-downing.

Take a look at the Roland Jet Phaser schematic.

There is a switch to choose between "Jet" and normal phasing in the middle of the circuit. Pulldowns are used in the same fashion as what was suggested here.